We are exposed to ultraviolet (UV) radiation on a daily basis. Depending on the exposure, UV-induced lesions such as (6-4)pyrimidine-pyrimidone photoproducts (6-4 PPs) and cyclobutane pyrimidine dimers (CPDs), can be formed by DNA absorption of UV. If such lesions are not properly repaired they can lead to damaged DNA, mutations and chromosome aberrations. More specifically, the formation and possible retention of UV-induced lesions due to problems in repair pathways could contribute to the development of skin cancer. The pathway responsible for the repair of UV-induced lesions is nucleotide excision repair (NER). Poly(ADP- ribose)polymerase-1 (PARP-1) is a zinc-finger protein with many functions within the cell, one in particular being its role in DNA repair pathways. Upon DNA damage it becomes activated and is able to form poly(ADP- ribose) moieties (pADPr) that assist in repair. PARP-1's role in base excision repair (BER), which repairs small, non-helix distorting lesions formed as a result of oxidation, deamination or alkylation, has been well established. Several papers have noted its direct interaction with proteins within the pathway (i.e. XRCC1, DNA polymerase 2, and DNA Ligase III). With regard to NER, there is growing evidence that PARP-1 may have a role in this pathway. Recent studies suggest that inhibition of PARP leads to the retention of pyrimidine dimers and other photolesions and we find similar results in human keratinocytes. While the data supporting PARP-1's involvement in NER is increasing, the mechanism of action has yet to be fully elucidated. There are several proteins that are involved in the early steps of NER, of note are XPC-hHR23B, DDB1 and XPA. In particular, XPA has been shown to contain a pADPr binding motif and its affinity for pADPr has been examined. Our hypothesis is that PARP-1 plays a role in the repair of ultraviolet induced DNA damage, and furthermore, its activation and subsequent formation of pADPr moieties allow it to interact with essential proteins in NER. We will test this hypothesis by 1) establishing whether PARP-1 deficiency alters the repair of ultraviolet induced DNA damage in keratinocytes using in vitro and in vivo systems, 2) identifying whether activation of PARP-1 will lead to the formation of pADPr subunits which act as a scaffold for early components of the NER pathway such as XPA and 3) establishing what effect loss of PARP-1 activity has on early NER components using molecular and biochemical approaches. Our preliminary findings showed that XPA is associated with pADPr moieties and immunoprecipitated with PARP-1 following UV exposure, supporting the hypothesis that pADPr may be acting as a scaffold for early components of NER. Obtaining information about PARP-1's role in the repair if UV-induced lesions will broaden our understanding of NER which may result in improved methods to prevent the retention of cancer causing lesions in the skin. PUBLIC HEALTH RELEVANCE: The NIEHS Strategic Plan specifically notes "the study of environmental factors that modify DNA damage, repair, and maintenance is an important area of investigation, particularly with regard to aging, cancer, and cell death." UVR is the major environmental agent contributing to skin cancer and this project is aimed at gaining a molecular understanding of PARP's role in DNA repair activities.